Nemo 33 is a recreational scuba diving center in Uccle, Belgium near Brussels that is home to the world's deepest swimming pool. The pool itself consists of a submerged structure with flat platforms at various depth levels. The pool has two large flat-bottomed areas at depth levels of 5 m (16 ft) and 10 m (32 ft), and a large circular pit descending to a depth of 33 m (108 ft). It is filled with 2,500,000 liters of non-chlorinated, highly filtered spring water maintained at 30 °C (86 °F) and contains several simulated underwater caves at the 10 m depth level.

There are numerous underwater windows that allow outside visitors to look into the pools at various depths. The complex was designed by Belgian diving expert John Beernaerts as a multi-purpose diving instruction, recreational, and film production facility, and opened in 2004.